1. Field of the Invention
The present invention relates to a tape loading mechanism, and more particularly to a pinch roller drive mechanism to guide a magnetic tape.
2. Description of Related Art
FIG. 1 is an oblique view of the constitution of a pinch roller unit of the prior art. In FIG. 1, numeral 1 denotes a pinch roller member which has a pinch roller 10 with which a magnetic tape is brought into contact., an L-shaped base 11 to hold the pinch roller 10, a hollow shaft 11a located at the center of the base 11, a rotary shaft 11b of the pinch roller 10 located at one end of the base 11, a U-shaped hook 11c located at the other end and a contact face 11d located at the opposite side of the hook 11c.
Numeral 2 denotes a rotary member to rotate the pinch roller member 1. The rotary member 2 has a hole 20a through which the hollow shaft 11a of the pinch roller member 1 is inserted, a projection 20b with which the contact face 11d comes in contact so as to prevent the pinch roller member 1 from rotating beyond a specified amount, hooks 20c and 20d, a projection 20e and a contact face 20f. A spring 4 is provided to link the hook 20c to the hook 11c of the pinch roller member 1, so that the force to press the pinch roller 10 against a capstan shaft is imparted to the pinch roller member 1. The capstan shaft is made to rotate by a capstan motor which supplies the force to drive the magnetic tape to run.
Numeral 3 denotes a sliding member which causes the pinch roller member 1 and the rotary member 2 to slide in the direction along the shaft, and has a hole 30a through which the hollow shaft 11a of the pinch roller member 1 is inserted, a hook 30b, a projection 30c to slide along a cam groove of a cam to be described later, and a contact face 30d. A spring 5 is provided to link the hook 30b to the hook 20d of the rotary member 2, so that the force to pull the pinch roller 10 away from the capstan shaft is imparted to the pinch roller member 1. The pinch roller member 1, the rotary member 2 and the sliding member 3 constitute the pinch roller unit.
FIG. 2 is a plan view and a side view of the cam of the prior art. In FIG. 2, numeral 6 denotes a cam having a hole 60f which penetrates through the cam in the direction of the axis thereof, and helical cam grooves 60a, 60b and 60c are cut thereon and a rim 60d and a gear 60e are provided below the cam grooves 60a, 60b and 60c. A cam follower 30c of the sliding member 3 slides along the cam grooves 60a, 60b and 60c.
Now the operation of the pinch roller unit having such a constitution as described above in a magnetic recording/reproducing apparatus will be described. FIG. 3 and FIG. 4 are schematic plan views of a tape drive system of an ordinary magnetic recording/reproducing apparatus. FIG. 3 shows the state before loading and FIG. 4 shows the state after loading. As shown in FIG. 3, a magnetic tape 9 is set in the magnetic recording/reproducing apparatus, and a guide pole 7 is moved in the direction of arrow 18c by a loading motor not shown in the drawing, thereby drawing the magnetic tape 9 toward a rotary drum 16 (as shown with a broken line 9a). Then guide rollers 15 comprising rollers 15a and guide poles 15b draw the magnetic tape 9 in the directions of arrows 18a and 18b and wind it around the rotary drum 16 as shown in FIG. 4.
The operation of the pinch roller during the loading of the magnetic tape 9 will be described below. As shown in FIG. 3, a rotary shaft 12a and a rotary shaft 12b are provided near the capstan shaft 8 and the hollow shaft 11a of the pinch roller unit is set movably in the rotary shaft 12a, while a cam 6 is set movably in the rotary shaft 12b. As the cam 6 is driven by the loading motor to rotate counterclockwise and the cam follower 30c of the sliding member 3 slides along the cam grooves 60a and 60b, the pinch roller unit moves sliding downward. FIG. 5 is a partially sectional view of the state of the pinch roller unit during the sliding motion. When the cam follower 30c reaches the cam groove 60c, the downward movement stops. Then as the projection 20e of the rotary member 2 rotates clockwise along the rim 60d of the cam 6, the spring 4 pulls the pinch roller member 1, thereby rotating the rotary member 2 and the pinch roller member 1 clockwise. At this time, the spring 5 is stretched.
As the pinch roller member 1 rotates clockwise as described above, the pinch roller 10 moves toward and comes in contact with the capstan shaft 8. Then the pinch roller member 1 is locked and only the rotary member 2 rotates clockwise so as to stretch the spring 4. The resilient force of the spring 4 imparts pressing force to the pinch roller 10, and thus the loading operation is completed.
When unloading, the cam 6 is driven by the loading motor to rotate clockwise, so that the rotary member 2 rotates counterclockwise to contract the spring 5. The contracting force of the spring 5 causes the pinch roller member 1 to rotate counterclockwise, thereby contracting the spring 4 and rotating the rotary member 2 counterclockwise. Thus, the pinch roller 10 is moved away from the capstan shaft 8.
The reason for the pinch roller 10 to move away from the capstan shaft 8 is because contracting force of the stretched spring 4 drives the pinch roller member 1 to rotate counterclockwise. The pinch roller 10, however, occasionally does not move away from the capstan shaft 8 smoothly due to the loading force of the spring 4. The magnetic tape 9 is damaged in such a case.
Also, the cam follower 30c occasionally does not slide smoothly along the cam groove 60b when the pinch roller unit moves sliding as shown in FIG. 5. This is because the weight of the pinch roller unit on the cam follower 30c side and that on the pinch roller 10 side is not well balanced, and because the cam and the pinch roller unit are linked via the cam follower 30c alone. In case the cam follower 30c does not slide smoothly along the cam groove 60b, there is a possibility of the cam follower 30c coming off the cam groove 60b.